setting up a span port

Connect with the console cable
Setup source and destination ports
https://supportforums.cisco.com/document/13891/how-configure-port-monitoring-span-catalyst-2940-2950-2955-2970-3550-or-3750-series
Run wire shark as admin

This example shows how to set up a SPAN session (session 1) for monitoring source port traffic to a destination port. First, any existing SPAN configuration for session 1 is cleared and then bidirectional traffic is mirrored from source port 1 to destination port 10:  

Switch(config)# no monitor session 1
Switch(config)# monitor session 1 source interface fastEthernet0/1
Switch(config)# monitor session 1 destination interface fastEthernet0/10 encapsulation dot1q
Switch(config)# end

This example shows how to configure the destination port for ingress traffic on VLAN 5 by using a security device that supports 802.1q encapsulation:  

Switch(config)# monitor session 1 destination interface Fa 0/5 encapsulation dot1q ingress vlan 5

This example shows how to clear any existing RSPAN configuration for session 1, configure RSPAN session 1 to monitor multiple source interfaces, and configure the destination RSPAN VLAN and the reflector-port:  

Switch(config)# no monitor session 1
Switch(config)# monitor session 1 source interface fastEthernet0/10 tx
Switch(config)# monitor session 1 source interface fastEthernet0/2 rx
Switch(config)# monitor session 1 source interface fastEthernet0/3 rx
Switch(config)# monitor session 1 source interface port-channel 102 rx
Switch(config)# monitor session 1 destination remote vlan 901 reflector-port fastEthernet0/1
Switch(config)# end 

This example shows how to configure VLAN 901 as the source remote VLAN and port 5 as the destination interface:   

Switch(config)# monitor session 1 source remote vlan 901
Switch(config)# monitor session 1 destination interface fastEthernet0/5
Switch(config)# end